Let editor workaround a case of inconsistency in compound scenes

doc/classes/EditorInterface.xml

@@ -179,6 +179,12 @@
 				Returns mesh previews rendered at the given size as an [Array] of [Texture2D]s.
 			</description>
 		</method>
+		<method name="mark_scene_as_unsaved">
+			<return type="void" />
+			<description>
+				Marks the current scene tab as unsaved.
+			</description>
+		</method>
 		<method name="open_scene_from_path">
 			<return type="void" />
 			<param index="0" name="scene_filepath" type="String" />

editor/editor_interface.cpp

@@ -36,6 +36,7 @@
 #include "editor/editor_resource_preview.h"
 #include "editor/editor_scale.h"
 #include "editor/editor_settings.h"
+#include "editor/editor_undo_redo_manager.h"
 #include "editor/filesystem_dock.h"
 #include "editor/gui/editor_run_bar.h"
 #include "editor/inspector_dock.h"
@@ -332,6 +333,10 @@ void EditorInterface::save_scene_as(const String &p_scene, bool p_with_preview)
 	EditorNode::get_singleton()->save_scene_to_path(p_scene, p_with_preview);
 }
 
+void EditorInterface::mark_scene_as_unsaved() {
+	EditorUndoRedoManager::get_singleton()->set_history_as_unsaved(EditorNode::get_editor_data().get_current_edited_scene_history_id());
+}
+
 // Scene playback.
 
 void EditorInterface::play_main_scene() {
@@ -430,6 +435,8 @@ void EditorInterface::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("save_scene"), &EditorInterface::save_scene);
 	ClassDB::bind_method(D_METHOD("save_scene_as", "path", "with_preview"), &EditorInterface::save_scene_as, DEFVAL(true));
 
+	ClassDB::bind_method(D_METHOD("mark_scene_as_unsaved"), &EditorInterface::mark_scene_as_unsaved);
+
 	// Scene playback.
 
 	ClassDB::bind_method(D_METHOD("play_main_scene"), &EditorInterface::play_main_scene);

editor/editor_interface.h

@@ -129,6 +129,7 @@ public:
 
 	Error save_scene();
 	void save_scene_as(const String &p_scene, bool p_with_preview = true);
+	void mark_scene_as_unsaved();
 
 	// Scene playback.
 

editor/editor_node.cpp

@@ -4103,6 +4103,13 @@ void EditorNode::add_io_error(const String &p_error) {
 	EditorInterface::get_singleton()->popup_dialog_centered_ratio(singleton->load_error_dialog, 0.5);
 }
 
+void EditorNode::add_io_warning(const String &p_warning) {
+	DEV_ASSERT(Thread::get_caller_id() == Thread::get_main_id());
+	singleton->load_errors->add_image(singleton->gui_base->get_theme_icon(SNAME("Warning"), SNAME("EditorIcons")));
+	singleton->load_errors->add_text(p_warning + "\n");
+	EditorInterface::get_singleton()->popup_dialog_centered_ratio(singleton->load_error_dialog, 0.5);
+}
+
 bool EditorNode::_find_scene_in_use(Node *p_node, const String &p_path) const {
 	if (p_node->get_scene_file_path() == p_path) {
 		return true;
@@ -6806,6 +6813,11 @@ EditorNode::EditorNode() {
 	ResourceLoader::set_error_notify_func(&EditorNode::add_io_error);
 	ResourceLoader::set_dependency_error_notify_func(&EditorNode::_dependency_error_report);
 
+	SceneState::set_instantiation_warning_notify_func([](const String &p_warning) {
+		add_io_warning(p_warning);
+		callable_mp(EditorInterface::get_singleton(), &EditorInterface::mark_scene_as_unsaved).call_deferred();
+	});
+
 	{
 		// Register importers at the beginning, so dialogs are created with the right extensions.
 		Ref<ResourceImporterTexture> import_texture;

editor/editor_node.h

@@ -731,6 +731,7 @@ public:
 	static bool has_unsaved_changes() { return singleton->unsaved_cache; }
 	static void disambiguate_filenames(const Vector<String> p_full_paths, Vector<String> &r_filenames);
 	static void add_io_error(const String &p_error);
+	static void add_io_warning(const String &p_warning);
 
 	static void progress_add_task(const String &p_task, const String &p_label, int p_steps, bool p_can_cancel = false);
 	static bool progress_task_step(const String &p_task, const String &p_state, int p_step = -1, bool p_force_refresh = true);

scene/resources/packed_scene.cpp

@@ -45,6 +45,10 @@
 
 #define PACKED_SCENE_VERSION 3
 
+#ifdef TOOLS_ENABLED
+SceneState::InstantiationWarningNotify SceneState::instantiation_warn_notify = nullptr;
+#endif
+
 bool SceneState::can_instantiate() const {
 	return nodes.size() > 0;
 }
@@ -380,7 +384,33 @@ Node *SceneState::instantiate(GenEditState p_edit_state) const {
 				//if node was not part of instance, must set its name, parenthood and ownership
 				if (i > 0) {
 					if (parent) {
-						parent->_add_child_nocheck(node, snames[n.name]);
+						bool pending_add = true;
+#ifdef TOOLS_ENABLED
+						if (Engine::get_singleton()->is_editor_hint()) {
+							Node *existing = parent->_get_child_by_name(snames[n.name]);
+							if (existing) {
+								// There's already a node in the same parent with the same name.
+								// This means that somehow the node was added both to the scene being
+								// loaded and another one instantiated in the former, maybe because of
+								// manual editing, or a bug in scene saving, or a loophole in the workflow
+								// (with any of the bugs possibly already fixed).
+								// Bring consistency back by letting it be assigned a non-clashing name.
+								// This simple workaround at least avoids leaks and helps the user realize
+								// something awkward has happened.
+								if (instantiation_warn_notify) {
+									instantiation_warn_notify(vformat(
+											TTR("An incoming node's name clashes with %s already in the scene (presumably, from a more nested instance).\nThe less nested node will be renamed. Please fix and re-save the scene."),
+											ret_nodes[0]->get_path_to(existing)));
+								}
+								node->set_name(snames[n.name]);
+								parent->add_child(node, true);
+								pending_add = false;
+							}
+						}
+#endif
+						if (pending_add) {
+							parent->_add_child_nocheck(node, snames[n.name]);
+						}
 						if (n.index >= 0 && n.index < parent->get_child_count() - 1) {
 							parent->move_child(node, n.index);
 						}

scene/resources/packed_scene.h

@@ -102,6 +102,14 @@ class SceneState : public RefCounted {
 
 	int _find_base_scene_node_remap_key(int p_idx) const;
 
+#ifdef TOOLS_ENABLED
+public:
+	typedef void (*InstantiationWarningNotify)(const String &p_warning);
+
+private:
+	static InstantiationWarningNotify instantiation_warn_notify;
+#endif
+
 protected:
 	static void _bind_methods();
 
@@ -201,6 +209,10 @@ public:
 	// Used when saving pointers (saves a path property instead).
 	static String get_meta_pointer_property(const String &p_property);
 
+#ifdef TOOLS_ENABLED
+	static void set_instantiation_warning_notify_func(InstantiationWarningNotify p_warn_notify) { instantiation_warn_notify = p_warn_notify; }
+#endif
+
 	SceneState();
 };